leap second coming June 30

What does the leap second mean for government IT?

On June 30, 2015, an extra second will be tacked on to the last minute of the day.  Known as a leap second, this occurrence will make standard civil time and all clocks synced to it read 23:59:60 before switching to July 1.

The Coordinated Universal Time (UTC) is adjusted to maintain its correlation with solar time because of irregularities in the Earth’s rotation, causing leap seconds. According to The International Earth Rotation and Reference Systems, there have been 25 leap seconds since 1972, the last one on June 30, 2012.

That's all well and good, but what about the clocks built into thousands of government IT systems?

The Department of Homeland Security released an informational guide earlier this year to alert and prepare federal, state, local and private organizations, as complications have occurred in the past on pre-determined adjustment dates.

To sustain normal operations, DHS suggests agencies make sure that all systems dependent on UTC are verified and have leap second insertion procedures in place and that all GPS receivers are aligned with the latest GPS interface specifications.

More important for IT departments, agencies must verify that their Network Time Protocol (NTP) servers and clients already have leap-second adjustment plans in place.

While all UTC clocks will implement the extra second , not all will use the same method.  According to the DHS, some systems receiving time through NTP could experience a delayed reaction to the update, depending on the software version.

Depending on the NTP server, a leap second flag may be installed that will inform the client software of the leap second occurrence and allow for an automatic adjustment. However, there is a possibility that some NTP servers may not have their leap second flag set up correctly (or at all), causing the servers to show the wrong time for up to a day and not account for the seconds.

To prevent this, the DHS recommends agencies update their NTP software on June 29 or 30 to ensure the most up-to-date installation.

Additionally, agencies should check with their cloud service providers, as three distinct methods could be used: the smear method; aligning with UTC; and counting the second or not as specified by the Portable Operating System Interface (POSIX) standards.

Some programs, like the Amazon Web Services (AWS) Management Console and Backend Systems and Google Cloud Platform Compute Engine, will apply the “smear” method.

Instead of adding the second or repeating it, Amazon and Google will spread out the second throughout the whole day. Google has opened a 20-hour “smear window” where it will slow all servers’ system clocks 14 parts per million, so that at the end of the window, the leap second is added and the system is in sync with civil time, according to a Google blog post.

Similarly, Amazon will spread the second out over a 24-hour window by also making each second a bit longer. According to Amazon’s post, AWS clocks could show a half-second behind or ahead of civil time during this process.  

For agencies using all of Google’s Compute Engine services, including its default NTP service, this will take place automatically. Those using an external time service may experience some discrepancies, like seeing a full-second step or several little steps.

If an external NTP service is used in conjunction with Google’s Compute Engine virtual machines, Google suggests verifying how that service handles the leap second and how it may affect applications or services. If possible, avoid using the external NTP service altogether, because mixing a smearing method with a non-smearing method could cause operational problems, according to Google.

Because Microsoft Windows follows POSIX standards, Windows Time Service will not react to a leap indicator when it receives a packet that includes a leap second.

Simply, Windows will not handle the second, so all POSIX-based computers will stay in sync with each other. According to Microsoft, after the leap second occurs, the NTP client running Windows Time Service will be a second ahead until the next time synchronization.  

It is important government agencies at all levels stay in-tune with their providers and procedures, as operational trouble has occurred in the past. Consult the DHS guide and specific NTP servers, and report operational challenges if they occur.

About the Author

Amanda Ziadeh is a former reporter/producer for GCN.


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